Amorphous carbon-silica composites bearing sulfonic acid as solid acid catalysts for the chemoselective protection of aldehydes as 1,1-diacetates and for N-, O- and S-acylations

Amorphous carbon-silica composites bearing sulfonic acid derived from inexpensive natural organic compounds (glucose, maltose, cellulose, chitosan and starch) were prepared by partial carbonization followed by sulfonation and their catalytic activity was evaluated for the protection of aldehydes as 1,1-diacetates and for N-, O- and S-acylations under solvent-free conditions. Different biomaterials have been chosen, with a view to select the most active solid acid catalyst. Carbon-silica composites were characterized by FTIR, XRD and elemental analysis. Sulfonated carbon-silica composite derived from starch was found to be the most active and could be recycled for several runs without loss of significant activity. It was also characterized by TGA, SEM and TEM.